The present invention relates to a static protective relay for protecting poly-phase AC power lines.
Detrimental phenomena from which the poly-phase AC power lines are protected are, for example, phase sequence, negative phase failure, overload, and the like. An approach for protecting the poly-phase AC lines from such phenomena, which has been proposed, employs a plurality of monofunctional static relays of contact and contactless types by the number corresponding to that of the phenomena. Those static protective relays are not standardized. Therefore, the approach needs a complicated system design and thus a complicated construction of the system.
Some of the conventional protective relays employ protective function checking circuits provided for the protective functions in one-to-one correspondence. This type relay, however, encounters a difficulty in processing the signals derived from the function checking circuits. Furthermore, it is difficult to make particularly a negative phase sequence detecting circuit contained therein static or solid-state in the fabrication. In this respect, the conventional static protective relays are unsatisfactory in their maintenance and inspection.